1. Field of the Invention
The present invention relates to a method for analyzing gas components, an apparatus for separating gas components, and a method for identifying the same.
2. Description of the Related Art
Currently, subjecting harvested fish to carbon monoxide treatment (CO treatment) using the method disclosed in, e.g., Patent Document 1, or using other methods is prohibited in Japan. Fresh fish imported from foreign countries is quantitatively analyzed by public inspection agencies using a method for analyzing carbon monoxide (hereinafter referred to as “method A”) contained in fresh fish, and a determination is made whether the fresh fish have been subjected to carbon monoxide treatment.
Specifically, method A is a method for quantitatively analyzing carbon monoxide containing fish, which entails adding twice the amount of water to 300 g of fish cut in thin slices; homogenizing the system for 1 minute under ice water using a homogenizer to obtain a sample fluid; placing 200 g of the sample fluid in a centrifuge and centrifuging the sample fluid at 10° C.; using the supernatant as the sample solution and subsequently placing 50 mL of the sample solution in a headspace bottle; adding 20 mL of 20% sulfuric acid, 5 mL of water, and 5 drops of octyl alcohol as an antifoaming agent; placing a cover having a silicone rubber stopper on the headspace bottle and vigorously shaking the bottle for 2 minutes; leaving the solution stationary for 10 minutes and then shaking the solution again for 1 minute; and immediately collecting the gas phase in the bottle into a gastight syringe and injecting the gas phase into a gas chromatograph to calculate the carbon monoxide concentration in the sample by using a separately prepared calibration curve.
When the quantitative value is 200 μg/kg or higher on the first day of testing, and the quantitative value two days later is clearly less than the quantitative value of the first day of testing, or when the quantitative value of the first day of testing is 500 (g/kg or higher, tuna or other types of fresh fish are determined to have been subjected to carbon monoxide treatment.
Professor Hidehiro Kumazawa and others of University of Toyama produced a plurality of uniform specimens from the same samples in order to ascertain the validity of method A, requested that the following three public inspection agencies perform an analysis of carbon monoxide in fish, and obtained the measurement results shown in TABLE 1.
TABLE 1Carbon monoxide concentration/(μg/kg)Inspection AgencySpecimen ASpecimen BSpecimen CInspection Agency A 75/1201,100/980  1,000/940  Inspection Agency B270/280350/420600/540Inspection Agency C640/470571/607352/364
There is a considerable measurement error, i.e., about 140%, from a minimum of 75 (g/kg and a maximum of 1,100 (g/kg, as shown in Table 1, and it is apparent from the experiment performed by Professor Hidehiro Kumazawa and others that method A has a reproducibility problem.
At least the following three problems can be given as causes of the measurement error.
1) Measurement Errors in the Homogenizing Stage
When a specimen is homogenized in ice water for 1 minute, it is presumed that all of the carbon monoxide is sealed within the sample solution, but this does not mean that homogenization occurs in the airtight space in particular. It is unavoidable that carbon monoxide present in the myoglobin (hereinafter referred to as “Mb”) of the fish is diffused throughout the gas.
2) Errors in the Centrifuging Stage
The fluid is centrifuged and the supernatant is used as the sample solution, but all of the carbon monoxide must be transferred to the supernatant at this time. However, since the solubility of carbon monoxide in an aqueous solution is very low, it is doubtful that all of the carbon monoxide has been dissolved in the supernatant. The undissolved carbon monoxide dissipates in the gas.
3) Errors in the Fabrication Stage of the Injection Gas Sample for Gas Chromatography
It is presumed that all of the carbon monoxide is transferred to the gas phase after a prescribed amount of the sample solution or other fluid is placed in a headspace bottle and the bottle is shaken and left standing, but a carbon monoxide concentration that is in balance with at least the carbon monoxide concentration in the gas phase remains in the liquid phase.
In view of the above, Professor Kumazawa solved the problem of method A by analyzing the gas components contained in the fish in the airtight circuit, and developed the highly reproducible Kumazawa Method (hereinafter referred to as the “KH method”). TABLE 2 shows the results of an analysis using the same samples as those shown in TABLE 1.
TABLE 2Carbon monoxide concentration/(μg/kg)Inspection AgencySpecimen ASpecimen BSpecimen CKH MethodD 1,490/1,3101,480/1,2401,220/1,040(Kumazawa Method)G 1,430/1,1801,470/1,2201,200/1,050*D: CO concentration measurement using a detector tube*G: CO concentration measurement using gas chromatography
The KH method for analyzing the carbon monoxide contained in fish is described in detail below.
The measuring apparatus of the KH method is shown in FIG. 1. A prescribed amount of fish is weighed, cut into 5 mm pieces, and used as samples. The samples are placed in boiling water 32 in flasks 31, and the gas components desorbed and diffused from the samples are collected into Tedlar bags 36 together with nitrogen gas injected from an injection port 35 connected by way of a pressure regulating value 33 and a flow meter 34. The water vapor emitted from the boiling water is condensed in a condenser 37 and returned to the flask. The gas components recovered in the Tedlar bags 36 are quantified using gas chromatography and gas sensors or detection tubes.
However, the KH method has the following problems.
In order to confirm that the gas components contained in the fish are diffused into the atmosphere, smoke treated tuna having a known surface area was placed into a container and the container was with 1 L of nitrogen, and the change in the carbon monoxide concentration in the container over time was measured. The results are shown in FIG. 2. The gas components can be confirmed to have diffused into the gas phase, which is the case of the measurement principle of method B as an officially authorized measurement method. Also, the amount diffused can be confirmed to be proportional to the surface area of the fish. It is therefore concluded that the gas components are diffused into the atmosphere when the samples are being prepared. When the gas components are recovered from the samples in the KH method, the components are recovered together with the nitrogen gas. Therefore, the gas components are diluted by the nitrogen gas, and it becomes difficult to quantify low-content gas components. Also, since the samples are 5 mm pieces, the method is laborious because a considerable amount of time is required to separate the gas components in the center of the samples.
[Patent Document 1] Japanese Laid-open Patent Application No. 2004-129627.